Does the a/c compressor need to come on for the heat to work?

The A/C compressor will usually come on when you set your climate control to "Defrost" to act as a dehumidifier to remove moisture from inside the cab area. If you cant afford to replace the A/C clutch assembly or the entire compressor at this time, simply unplug the connector at the compressor clutch and secure it away from the belts, moving parts or heat sources that could damage the plug. Doing this will keep the A/C clutch from being energized. The problem is not solved but it will stop the screaming noise and power loss you spoke of.

just use the floor or dash vent heat.dont use the windshield defrost as heat cause that will kick on the compressor.